Initializing method and data transmitter

ABSTRACT

A first initialization pattern signal is a signal in which a maximum signal level and a minimum signal level appear alternately, and a second initialization pattern signal is a signal in which all signal levels appear in a predetermined arrangement. In a ring-shaped network including plural stages of data transmission apparatuses ( 100 ), a transmission unit ( 110 ) of each data transmission apparatus outputs the first initialization pattern signal successively to a next-stage data transmission apparatus at turn-on of power or immediately after reset, and a reception unit ( 120 ) establishes clock synchronization on the basis of the first initialization pattern signal received. When synchronization is established in all of the data transmission apparatuses, the transmission unit ( 110 ) outputs the second initialization pattern signal successively to the next-stage data transmission apparatus, and the reception unit ( 120 ) sets evaluation levels for the respective signal levels on the basis of the received second initialization pattern signal, and transmission/reception of data is started when evaluation levels are set in all of the data transmission apparatuses.

TECHNICAL FIELD

[0001] The present invention relates to an initialization method and adata transmission apparatus in a ring-shaped network and, moreparticularly, to those for generating an initialization pattern signalfor establishing synchronization and an initialization pattern signalfor setting evaluation levels, and performing establishment ofsynchronization and setting of evaluation levels on the basis of theseinitialization pattern signals.

BACKGROUND ART

[0002] As a conventional data transmission method, there is a method fortransmitting data while converting data symbols into signal levels of anelectric signal or an optical signal. During such data transmission,when the signal being transmitted continuously takes a constant signallevel or when it repeatedly takes a specific pattern of signal levels, adata reception apparatus cannot detect the magnitudes of original signallevels, and therefore, it cannot perform accurate data reception. As amethod for avoiding this problem there is a scrambling method if whichdata symbols to be transmitted are evenly assigned to all signal levelsby adding random numbers to digital data to be transmitted.

[0003]FIG. 8 is a diagram illustrating the construction of a datareceiver for CATV (CABLE TELEVISION). As shown in FIG. 8, the datareceiver for CATV is provided with a tuner 801, a down converter 802, anA/D converter 803, a detector 804, a digital filter 805, an evaluationunit 806, a descrambler 807, a clock reproduction unit 808, and a gaindetector 809.

[0004] Since CATV data are scrambled, all signal levels are almostevenly included in received data symbols. Usually, quadrature amplitudemodulation such as 16 QAM or 64 QAM is employed as a CATV transmissionmethod, and a coaxial cable is employed as a transmission path.

[0005] Next, the operation of the CATV data receiver so constructionwill be described.

[0006] A QAM signal received through a coaxial cable isfrequency-converted through the tuner 801 and the down converter 802,and one channel of QAM signal is input to the A/D converter 803. Thisone channel of QAM signal is converted into a digital signal by the A/Dconverter 803, and an I-axis signal and a Q-axis signal are separatedand demodulated by the detector 804. After removal of noises through thedigital filter 805, data symbols are decoded by the evaluation unit 806,and descrambled by the descrambler 807 thereby obtaining data. Further,the clock reproduction unit 808 establishes synchronization by detectingclock shift in a transmission unit from the I-axis signal and the Q-axissignal.

[0007] Since the data are scrambled, all signal levels are almost evenlyincluded in the received signal. The gain detector 809 detects thereceived signal level, and performs gain control so that the signallevel is correctly decoded by the evaluation unit 806. That is, the gaindetector 809 feeds the received signal level back to the down converter802 so as to correlate the signal level to a stored threshold value,thereby performing gain control. Further, the down converter 802performs gain control for the tuner 801 as desired.

[0008] However, when performing scrambling or descrambling, a data framefor adjusting data timing is needed, and therefore, scrambling cannot beperformed on data in a format having no data frame. Moreover, even whenscrambling can be carried out, if a data pattern to be transmittedmatches a random number sequence used for scrambling, the same signallevel continues undesirably.

[0009] Furthermore, since, in the conventional data transmission method,it is necessary to receive all signal levels to perform gain control,the data should be scrambled to be averaged. However, when a pattern ofsignal in which only a specific signal level appears continues, gaincontrol becomes impossible, and accurate evaluation of signal levelscannot be carried out.

[0010] Moreover, also in a network in which plural stages of datatransmission/reception apparatuses each having a transmission unit fortransmitting data and a reception unit for receiving data are connectedin a ring shape, the reception unit of each data transmission/receptionapparatus has the same problem as in the above-described data receiver.

[0011] The present invention is made to solve the above-describedproblems and has for its object to provide an initialization method anda data transmission apparatus, which realize accurate data transmissionindependent of signal levels and patterns, without scrambling data to betransmitted, in multi-valued transmission.

DISCLOSURE OF THE INVENTION

[0012] In order to solve the above-described problems, according to thepresent invention (claim 1), there is provided an initialization methodto be used in a network in which plural stages of data transmissionapparatuses each performing data transmission while assigning one ormore bits of data as one data symbol to a signal level, are connected ina ring shape, wherein one of the data transmission apparatuses is amaster data transmission apparatus, while the other data transmissionapparatuses are slave data transmission apparatuses; at turn-on of poweror immediately after reset, the master data transmission apparatusoutputs a first initialization pattern signal to a slave datatransmission apparatus in the next stage; the next-stage slave datatransmission apparatus establishes clock synchronization on receipt ofthe first initialization pattern signal; when clock synchronization isestablished, the next-stage slave data transmission apparatus outputsthe first initialization pattern signal to a slave data transmissionapparatus in the next stage; when synchronization is established in allof the slave data transmission apparatuses and the master datatransmission apparatus which are connected in the network, the masterdata transmission apparatus outputs a second initialization patternsignal to the next-stage slave data transmission apparatus; thenext-stage slave data transmission apparatus receives the secondinitialization pattern signal, sets an evaluation level for each signallevel, and outputs the second initialization pattern to a datatransmission apparatus in the next stage; and transmission/reception ofdata is started after evaluation levels of data are set in all of theslave data transmission apparatuses and the master data transmissionapparatus which are connected in the network.

[0013] Further, according to the present invention (claim 2), in theinitialization method as defined in claim 1, the first initializationpattern signal is a signal in which a maximum signal level and a minimumsignal level appear alternately; and the second initialization patternsignal is a signal in which all signal levels appear in a predeterminedarrangement.

[0014] Further, according to the present invention (claim 3), in theinitialization method as defined in claim 2, the first initializationpattern signal is a signal in which a signal for discriminating betweenthe first initialization pattern signal and the second initializationpattern signal appears at the end.

[0015] Further, according to the present invention (claim 4), in theinitialization method as defined in claim 2, the second initializationpattern signal is a signal in which a signal for discriminating betweenthe first initialization pattern signal and the second initializationpattern signal appears at the beginning.

[0016] Further, according to the present invention (claim 5), there isprovided a data transmission apparatus which is connected in aring-shaped network, and performs data transmission while assigning oneor more bits of data as one data symbol to a signal level, and theapparatus comprises: a first initialization pattern output unit foroutputting a first initialization pattern signal for establishing clocksynchronization to a data transmission apparatus connected in the nextstage; a second initialization pattern output unit for outputting asecond initialization pattern signal for setting an evaluation level bywhich the signal level is subjected to threshold evaluation, to the datatransmission apparatus connected in the next stage; and asynchronization establishment unit for receiving the firstinitialization pattern signal transmitted from a data transmissionapparatus connected in the previous stage, and performing clockreproduction to establish synchronization; whereintransmission/reception of data is started after synchronization isestablished on receipt of the first initialization pattern signal, andevaluation levels of data are set on receipt of the secondinitialization pattern signal.

[0017] Further, according to the present invention (claim 6), the datatransmission apparatus as defined in claim 5 is a master datatransmission apparatus in which the first initialization pattern outputunit outputs the first initialization pattern signal at turn-on of poweror immediately after reset, and the second initialization pattern outputunit outputs the second initialization pattern signal whensynchronization is established in all of the data transmissionapparatuses.

[0018] Further, according to the present invention (claim 7), the datatransmission apparatus as defined in claim 5 is a slave datatransmission apparatus in which the first initialization pattern outputunit outputs the first initialization pattern signal whensynchronization is established, and the second initialization patternoutput unit outputs the second initialization pattern signal when thebeginning of the second initialization pattern signal is received.

[0019] As described above, according to the present invention (claim 1),there is provided an initialization method to be used in a network inwhich plural stages of data transmission apparatuses each performingdata transmission while assigning one or more bits of data as one datasymbol to a signal level, are connected in a ring shape, wherein one ofthe data transmission apparatuses is a master data transmissionapparatus, while the other data transmission apparatuses are slave datatransmission apparatuses; at turn-on of power or immediately afterreset, the master data transmission apparatus outputs a firstinitialization pattern signal to a slave data transmission apparatus inthe next stage; the next-stage slave data transmission apparatusestablishes clock synchronization on receipt of the first initializationpattern signal; when clock synchronization is established, thenext-stage slave data transmission apparatus outputs the firstinitialization pattern signal to a slave data transmission apparatus inthe next stage; when synchronization is established in all of the slavedata transmission apparatuses and the master data transmission apparatuswhich are connected in the network, the master data transmissionapparatus outputs a second initialization pattern signal to thenext-stage slave data transmission apparatus; the next-stage slave datatransmission apparatus receives the second initialization patternsignal, sets an evaluation level for each signal level, and outputs thesecond initialization pattern to a data transmission apparatus in thenext stage; and transmission/reception of data is started afterevaluation levels of data are set in all of the slave data transmissionapparatuses and the master data transmission apparatus which areconnected in the network. Therefore, synchronization of the respectivedata transmission apparatuses can be established, and evaluation levelsof data symbols can be set. Further, since evaluation levels are set onthe basis of the voltage values of the respective signal levels includedin the second initialization pattern signal, evaluation levels can beset in accordance with the transmission path, whereby accurate datareception can be carried out without being affected by the pattern ofdata symbols to be transmitted or the values of the received signallevels. Moreover, since each data transmission apparatus can transmitthe second initialization pattern signal to the next-stage datatransmission apparatus upon receipt of the beginning of the secondinitialization pattern, setting of evaluation levels and initializationof the ring-shaped network can be carried out more speedily.

[0020] Further, according to the present invention (claim 2), in theinitialization method as defined in claim 1, the first initializationpattern signal is a signal in which a maximum signal level and a minimumsignal level appear alternately; and the second initialization patternsignal is a signal in which all signal levels appear in a predeterminedarrangement. Therefore, evaluation levels of data symbols can be setafter synchronization is established by clock reproduction. Further, allof the signal levels can be obtained without scrambling the secondinitialization pattern signal.

[0021] Further, according to the present invention (claim 3), in theinitialization method as defined in claim 2, the first initializationpattern signal is a signal in which a signal for discriminating betweenthe first initialization pattern signal and the second initializationpattern signal appears at the end. Therefore, the beginning of thesecond initialization pattern signal can be detected, whereby the secondinitialization pattern signal can be transmitted to the next-stage datatransmission apparatus without waiting for reception of the whole secondinitialization pattern signal.

[0022] Further, according to the present invention (claim 4), in theinitialization method as defined in claim 2, the second initializationpattern signal is a signal in which a signal for discriminating betweenthe first initialization pattern signal and the second initializationpattern signal appears at the beginning. Therefore, the beginning of thesecond initialization pattern signal can be detected, whereby the secondinitialization pattern signal can be transmitted to the next-stage datatransmission apparatus without waiting for reception of the whole secondinitialization pattern signal.

[0023] Further, according to the present invention (claim 5), there isprovided a data transmission apparatus which is connected in aring-shaped network, and performs data transmission while assigning oneor more bits of data as one data symbol to a signal level, and theapparatus comprises: a first initialization pattern output unit foroutputting first initialization pattern signal for establishing clocksynchronization to a data transmission apparatus connected in the nextstage; a second initialization pattern output unit for outputting asecond initialization pattern signal for setting an evaluation level bywhich the signal level is subjected to threshold evaluation, to the datatransmission apparatus connected in the next stage; and asynchronization establishment unit for receiving the firstinitialization pattern signal transmitted from a data transmissionapparatus connected in the previous stage, and performing clockreproduction to establish synchronization; whereintransmission/reception of data is started after synchronization isestablished on receipt of the first initialization pattern signal, andevaluation levels of data are set on receipt of the secondinitialization pattern signal. Therefore, synchronization of therespective data transmission apparatuses can be established, andevaluation levels of data symbols can be set. Further, since evaluationlevels are set according to the voltage values of the respective signallevels included in the second initialization pattern signal, evaluationlevels can be set in accordance with the transmission path, wherebyaccurate data reception can be carried out without being affected by thepattern of data symbols to be transmitted or the values of the receivedsignal levels.

[0024] Further, according to the present invention (claim 6), the datatransmission apparatus as defined in claim 5 is a master datatransmission apparatus in which the first initialization pattern outputunit outputs the first initialization pattern signal at turn-on of poweror immediately after reset, and the second initialization pattern outputunit outputs the second initialization pattern signal whensynchronization is established in all of the data transmissionapparatuses. Therefore, the ring-shaped network can be initialized.

[0025] Further, according to the present invention (claim 7), the datatransmission apparatus as defined in claim 5 is a slave datatransmission apparatus in which the first initialization pattern outputunit outputs the first initialization pattern signal whensynchronization is established, and the second initialization patternoutput unit outputs the second initialization pattern signal when thebeginning of the second initialization pattern signal is received.Therefore, the ring-shaped network can be initialized. Further, sincethe data transmission apparatus can transmit the second initializationpattern signal to the next-stage data transmission apparatus uponreceipt of the beginning of the second initialization pattern signal,setting of evaluation levels and initialization of the ring-shapednetwork can be carried out more speedily.

BRIEF DESCRIPTION OF THE DRAWINGS

[0026]FIG. 1 is a block diagram illustrating the construction of a datatransmission apparatus according to a first embodiment of the presentinvention.

[0027]FIG. 2 is a block diagram illustrating the construction of aring-shaped network in which the data transmission apparatus accordingto the first embodiment of the invention is connected.

[0028]FIG. 3 is a diagram for explaining a method for converting datasymbols into signal levels according to the first embodiment of theinvention.

[0029]FIG. 4 is a diagram illustrating an example of a waveform on atransmission path according to the first embodiment of the invention.

[0030]FIG. 5 is a diagram illustrating a first initialization patternsignal according to the first embodiment of the invention.

[0031]FIG. 6 is a diagram illustrating an example of a signal to be usedin initialization according to the first embodiment of the invention.

[0032]FIG. 7 is a flowchart for explaining the operation of thering-shaped network according to the first embodiment of the invention.

[0033]FIG. 8 is a block diagram illustrating the construction of a CAVTreceiver as a conventional data transmission apparatus.

BEST MODE TO EXECUTE THE INVENTION

[0034] Hereinafter, an embodiment of the present invention will bedescribed with reference to the drawings. However, the embodimentdescribed hereinafter is merely an example, and the present invention isnot restricted thereto.

[0035] (Embodiment 1)

[0036] An initialization method described in claims 1 to 4 of thepresent invention, and a data transmission apparatus described in claims5 to 7 will be described as a first embodiment with reference to thedrawings.

[0037]FIG. 1 is a block diagram illustrating the construction of a datatransmission apparatus according to the first embodiment.

[0038] As shown in FIG. 1, a data transmission apparatus 100 accordingto the first embodiment is provided with a transmission unit foroutputting data, a reception unit 120 for receiving the data outputtedfrom the transmission unit 110, and a transmission path 130 fortransmitting the data outputted from the transmission unit 110.

[0039] The transmission unit 110 is provided with a data mapping unit111 for mapping a digital signal to be transmitted to eight signallevels at every symbol timing; a first initialization pattern generator112 for generating a first initialization pattern signal; a secondinitialization pattern generator 113 for generating a secondinitialization pattern signal; a selector 114 for selecting a signal tobe transmitted from among the signal levels to which the digital signalis mapped, the first initialization pattern signal, and the secondinitialization pattern signal; a digital filter 115 which allows a bandof frequency components corresponding to half of the symbol rate topass; a D/A converter 116 for converting digital data into an analogsignal; a low-pass filter 117 for removing noises outside the signalband of the signal to be transmitted; and a driver 118 for amplifyingthe signal intensity, and outputting the signal to the transmission path130.

[0040] On the other hand, the reception unit 120 is provided with areceiver 121 for receiving the signal; a low-pass filter 122 forremoving noises outside the signal band; an A/D converter 123 forconverting the signal into digital signal; a digital filter 124 whichallows a band of frequency components corresponding to half of thesymbol rate to pass; a clock reproduction unit 126 for establishingsynchronization; an evaluation level holding unit 127 for settingevaluation levels corresponding to the respective signal levels, andholding them; an evaluation unit 125 for performing threshold evaluationon the respective signal levels on the basis of the signal levelevaluation values which are stored in the evaluation level holding unit127, and decoding the data symbols; a synchronization/initializationpattern detector 128 for detecting establishment of synchronization, andthe beginning of the second initialization pattern signal; and atransmission data controller 129 for outputting a transmission datacontrol signal which instructs transmission of a signal selected fromamong the signal outputted from the data mapping unit 111, the firstinitialization pattern signal, and the second initialization patternsignal.

[0041] Further, a coaxial cable or a twisted-pair cable is used as thetransmission path 130. When the transmission path 130 is a twisted-paircable, a differential output driver should be used as the driver 118.

[0042]FIG. 2 is a block diagram illustrating the construction of aring-shaped network according to the first embodiment.

[0043] As shown in FIG. 2, the ring-shaped network according to thefirst embodiment is provided with n stages of data transmissionapparatuses 100, and these data transmission apparatuses are connectedin a ring shape such that a signal outputted from a transmission unit110 of a previous-stage data transmission apparatus 100 is received by areception unit 120 of a next-stage data transmission apparatus 100, anda signal outputted from a transmission unit 110 of a final-stage datatransmission apparatus 100 is received by a reception unit 120 of aninitial-stage data transmission apparatus 100.

[0044] All of the data transmission apparatuses are identical inconstruction to the data transmission apparatus 100. That is, a firstdata transmission apparatus 100 a has a transmission unit 110 a, areception unit 120 a, and a transmission path 130 a. The transmissionunit 110 a includes a data mapping unit 111 a, a first initializationpattern generator 112 a, a second initialization pattern generator 113a, a selector 114 a, a digital filter 115 a, a D/A converter 116 a, alow-pass filter 117 a, and a driver 118 a. The reception unit 120 a hasa receiver 121 a, a low-pass filter 122 a, an A/D converter 123 a, adigital filter 124 a, an evaluation unit 125 a, a clock reproductionunit 126 a, an evaluation level holding unit 127 a, asynchronization/initialization pattern detector 128 a, and atransmission data controller 129 a.

[0045] Likewise, a second data transmission apparatus 100 b has atransmission unit lob, a reception unit 120 b, and a transmission path130 b. The transmission unit 110 b includes a data mapping unit 111 b, afirst initialization pattern generator 112 b, a second initializationpattern generator 113 b, a selector 114 b, a digital filter 115 b, a D/Aconverter 116 b, a low-pass filter 117 b, and a driver 118 b. Thereception unit 120 b has a receiver 121 b, a low-pass filter 122 b, anA/D converter 123 b, a digital filter 124 b, an evaluation unit 125 b, aclock reproduction unit 126 b, an evaluation level holding unit 127 b, asynchronization/initialization pattern detector 128 b, and atransmission data controller 129 b.

[0046] Further, a final-stage data transmission apparatus 100 n has atransmission unit 110 n, a reception unit 120 n, and a transmission path130 n. The transmission unit 110 n includes a data mapping unit 111 n, afirst initialization pattern generator 112 n, a second initializationpattern generator 113 n, a selector 114 n, a digital filter 115 n, a D/Aconverter 116 n, a low-pass filter 117 n, and a driver 118 n. Thereception unit 120 n has a receiver 121 n, a low-pass filter 122 n, anA/D converter 123 n, a digital filter 124 n, and evaluation unit 125 n,a clock reproduction unit 126 n, an evaluation level holding unit 127 n,a synchronization/initialization pattern detector 128 n, and atransmission data controller 129 n.

[0047] The transmission unit 110 a of the first data transmissionapparatus 10 a and the reception unit 120 b of the second datatransmission apparatus 100 b are connected with the transmission path130 a, the transmission unit 110 b of the second data transmissionapparatus 100 b and the reception unit 120 c of the third datatransmission apparatus 100 c are connected with the transmission path130 b, and the transmission unit 110 n of the final-stage datatransmission apparatus 100 n and the reception unit 120 a of the firstdata transmission apparatus 100 a are connected with the transmissionpath 130 n, thereby constituting the ring-shaped network.

[0048] The first data transmission apparatus 100 a is a master whichoutputs data at turn-on of power or immediately after reset, and thesecond to n-th data transmission apparatuses 100 b to 100 n are slaveswhich are operated according to the data outputted from the master.

[0049] The transmission data controller 129 a of the first datatransmission apparatus is supplied with a signal indicating that thisapparatus 100 a is a master, and each of the transmission datacontrollers 129 b to 129 n of the second to n-th data transmissionapparatuses 100 b to 100 n is supplied with a signal indicating thatthis apparatus is a slave.

[0050] Based on the signal indicating that the apparatus is a master,the transmission data controller 129 a outputs a transmission datacontrol signal instructing transmission of the second initializationpattern signal when synchronization of the reception unit 120 a isestablished. Further, on receipt of the beginning of the signal forrecognizing the start of the second initialization pattern signal, thetransmission data controller 129 a outputs a transmission data controlsignal instructing transmission of the signal that is mapped in the datamapping unit 111 a.

[0051] On the other hand, based on the signal indicating that theapparatus is a slave, each of the transmission data controllers 129 b to129 n outputs a transmission data control signal indicating transmissionof the first initialization pattern signal when synchronization of eachof the reception units 120 b to 120 n is established. Further, onreceipt of the beginning of the signal for recognizing the start of thesecond initialization pattern signal, the transmission data control unitoutputs a transmission data control signal instructing transmission ofthe second initialization pattern signal.

[0052] Next, the operation of the data transmission apparatus 100 willbe described.

[0053] As shown in FIG. 3, the data mapping unit 111 maps eight kinds of3-bit data symbols to eight signal levels. FIG. 3 is a conversion tableillustrating conversion from data symbols to signal levels (mappingvalues), in which 3-bit data symbols are mapped to any of eight signallevels, “−7”, “−5”, “−3”, “−1”, “+1”, “+3”, “+5”, and “+7”.

[0054] Hereinafter, the data transmission apparatus 100 performing such8-value transmission will be described.

[0055] Next, the operation of the data transmission apparatus 100 soconstructed will be described.

[0056] Initially, ordinary data transmission will be described. Inordinary data transmission, every three bits of digital data beingtransmitted in the transmission unit 110 are mapped to one of eightsignal levels according to the conversion table shown in FIG. 3, atevery symbol timing. Since the selector 114 is supplied with thetransmission data control signal instructing transmission of the signalfrom the data mapping unit 111, the selector 114 selects the signal thatis mapped in the data mapping unit 111, and inputs this signal to thedigital filter 115. The digital filter 115 is a low-pass filter thatallows a band of frequency components corresponding to half of thesymbol rate to pass, and actually it is constituted so as to haveappropriate roll-off characteristics in combination with the digitalfilter 124 of the reception unit 120. The signal that has been passedthrough the digital filter 115 is converted into an analog signal by theD/A converter 116, and the analog signal is passed through the low-passfilter 117, whereby a signal within A hand that is slightly larger thanhalf of the symbol rate is obtained, and a signal having no interferencebetween adjacent codes is obtained at readout timing. Thereby, datatransmission in the finite band can be carried out. Then, the driver 118amplifies the signal intensity of this signal, and outputs the signal tothe transmission path 130.

[0057] An example of a waveform on the transmission path is shown inFIG. 4. In the example of FIG. 4, the signal levels are transmitted inorder of “+7”, “+1”, “−1”, “+1”, “−7”, . . . , and data symbols“111(+7)”, “100(+1)”, “011(−1)”, “100(+1)”, “000(−7)”, . . . aretransmitted.

[0058] The signal so transmitted is received by the reception unit 120.

[0059] In the reception unit 120, the receiver 121 receives the signal,and the low-pass filter 122 removes noises outside the signal band.Then, the A/D converter 123 converts the signal into digital data, andthe digital data is passed through the digital filter 124. The digitalfilter 124 has roll-off characteristics in combination with the digitalfilter 115 of the transmission unit 110, and it converts the digitaldata into a signal that can be received without being affected byinterference between adjacent codes, at appropriate timing. Thereafter,the evaluation unit 125 decodes the data symbols on the basis of thesignal level evaluation values which are stored in the evaluation levelholding unit 127. The clock reproduction unit 126 reproduces a clockfrom the received data, and establishes synchronization when decodingthe data symbols. Ordinary data transmission is carried out as describedabove.

[0060] Next, the initialization method by the data transmissionapparatus 100 that operates as above will be described.

[0061]FIG. 5 is a diagram illustrating the first initialization patternsignal. FIG. 6 is a diagram illustrating an example of a signal to beused for initialization.

[0062] A signal to be used for initialization includes signal componentsas follows: a first initialization pattern signal including a frequencycomponent equal to ½ of the symbol rate, in which a maximum amplitudelevel and a minimum amplitude level appear alternately (portion A shownin FIGS. 5 and 6); a signal for recognizing the start of a secondinitialization pattern signal, which has a maximum amplitude level(portion B shown in FIG. 6); and a second initialization pattern signalin which all signal levels appear in an arrangement that ispredetermined by the transmission unit 110 and the reception unit 120(portion C shown in FIG. 6).

[0063] The first initialization pattern signal is generated by the firstinitialization pattern generator 112. On the other hand, the signal forrecognizing the start of the second initialization pattern signal, andthe second initialization pattern signal are generated by the secondinitialization pattern generator 113. FIG. 6 shows an example in which aportion of a predetermined arrangement of signal levels in the secondinitialization pattern signal is “+5”, “+1, “−5”, “−1”, “+3”, “−3”,“+5”, “−7”. This evaluation level setting pattern signal is desired tobe a signal such as a PN pattern, in which all of the signal levels areevenly included, and various patterns appear.

[0064] Further, the transmission data controller 129 outputs, to theselector 114, a transmission data control signal indicating transmissionof any of the signal from the data mapping unit 111, the firstinitialization pattern signal, and the second initialization patternsignal, on the basis of the output from thesynchronization/initialization pattern detector 128. Then, the selectorselects a signal to be transmitted, on the basis of the transmissiondata control signal.

[0065] Next, the operation of the ring-shaped network so constitutedwill be described with reference to FIG. 7.

[0066]FIG. 7 is a flowchart for explaining the operation of thering-shaped network. Here, a ring-shaped network comprising three stagesof data transmission apparatuses 100 a to 100 c will be described.

[0067] At turn-on of power or immediately after reset, the transmissionunit 110 a of the first data transmission apparatus 10 a transmits thefirst initialization pattern signal. That is, the selector 114 a selectsthe first initialization pattern signal generated by the firstinitialization pattern generator 112 a, and inputs this signal to thedigital filter 115 a. Then, the first initialization pattern signal isoutput to the transmission path 130 a in like manner as the ordinarydata transmission (step S201).

[0068] The first initialization pattern signal so transmitted isreceived by the reception unit 120 b of the second data transmissionapparatus 100 b. When the reception unit 120 b receives the firstinitialization pattern signal, initially, the clock reproduction unit126 b performs clock reproduction. When thesynchronization/initialization pattern detector 128 b detects thatsynchronization is established, a synchronization detection signal isoutput to the transmission data controller 129 b. Then, the transmissiondata control unit 129 b outputs a transmission data control signalinstructing transmission of the first initialization pattern signal, tothe selector 114 b of the transmission unit 110 b (step S202).

[0069] When the transmission data control signal instructingtransmission of the first initialization pattern signal is input to theselector 114 b, the transmission unit 110 b transmits the firstinitialization pattern signal. That is, the selector 114 b selects thefirst initialization pattern signal generated by the firstinitialization pattern generator 112 b, and inputs this signal to thedigital filter 115 b. Then, the first initialization pattern signal isoutput to the transmission path 130 b in like manner as the ordinarydata transmission (step S203).

[0070] The first initialization pattern signal so transmitted isreceived by the reception unit 120 c of the third data transmissionapparatus 100 c. When the reception unit 120 c receives the firstinitialization pattern signal, initially, the clock reproduction unit126 c performs clock reproduction, and thesynchronization/initialization pattern detector 128 c detects thatsynchronization is established. After establishment of synchronization,the transmission data control unit 129 c outputs a transmission datacontrol signal instructing transmission of the first initializationpattern signal, to the selector 114 c of the transmission unit 110 c(step S204).

[0071] When the transmission data control signal instructingtransmission of the first initialization pattern signal is input to theselector 114 c, the transmission unit 110 c transmits the firstinitialization pattern signal. That is, the selector 114 c selects thefirst initialization pattern signal generated by the firstinitialization pattern generator 112 c, and inputs this signal to thedigital filter 115 c. Then, the first initialization pattern signal isoutput to the transmission path 130 c in like manner as the ordinarydata transmission (step S205).

[0072] The first initialization pattern signal so transmitted isreceived by the reception unit 120 a of the first data transmissionapparatus 100 a. When the reception unit 120 a receives the firstinitialization pattern signal, initially, the clock reproduction unit126 a reproduces a clock, and then the synchronization/initializationpattern detector 128 a detects that synchronization is established.Thereafter, the transmission data control unit 129 a outputs atransmission data control signal instructing transmission of the secondinitialization pattern signal, to the selector 114 a of the transmissionunit 110 a (step S206).

[0073] When the transmission data control signal instructingtransmission of the second initialization pattern signal is input to theselector 114 a of the first data transmission apparatus 10 a, theselector 114 a selects, as a transmission signal, the secondinitialization pattern signal generated by the second initializationpattern generator 113 a, and inputs this signal to the digital filter115 a. Then, the second initialization pattern signal and the signal forrecognizing the start of the second initialization pattern signal areoutput to the transmission path 130 a in like manner as for the firstinitialization pattern signal (step S207).

[0074] Thereafter, output of data is continued until all of the signallevels of the second initialization pattern signal are output to thetransmission path 130 a (step S208).

[0075] The second initialization pattern signal so transmitted isreceived by the reception unit 120 b of the second data transmissionapparatus 100 b. When the synchronization/initialization patterndetector 128 b detects the beginning of the signal for recognizing thestart of the second initialization pattern signal, the transmission datacontroller 129 b outputs a transmission data control signal instructingtransmission of the second initialization pattern signal, to theselector 114 b of the transmission unit 110 b (step S209).

[0076] When the reception unit 120 b receives the signal for recognizingthe start of the second initialization pattern signal and, further, thesecond initialization pattern signal, the evaluation level holding unit127 b performs threshold evaluation for the signal levels to setevaluation levels to be used when decoding the signal levels to the datasymbols. The evaluation level holding unit 127 b detects the voltagevalues of the respective signal levels included in the secondinitialization pattern signal. That is, the voltage values of therespective signal levels “+7”, “+5”, “+3”, “+1”, “−7”, “−5”, “−3”, and“−1” are obtained. Then, the evaluation level holding unit 127 b setsthe evaluation levels for the respective signal levels on the basis ofthe obtained voltage values of the signal levels, and holds theseevaluation levels (step S210).

[0077] When the transmission data control signal instructingtransmission of the second initialization pattern signal is input to theselector 114 b, the transmission unit 110 b transmits the secondinitialization pattern signal. That is, the selector 114 b selects thesecond initialization pattern signal generated by the secondinitialization pattern generator 113 b, and inputs this signal to thedigital filter 115 b. Then, the signal for recognizing the start of thesecond initialization pattern signal and the second initializationpattern signal are output to the transmission path 130 b in like manneras for the first initialization pattern signal (step S211).

[0078] When the reception unit 120 b has received all of the signallevels of the second initialization pattern signal, and setting of theevaluation levels has been completed, the transmission data controller129 b outputs a transmission data control signal instructingtransmission of the signal which is mapped in the data mapping unit 111b, to the selector 114 b of the transmission unit 110 b (step S212).

[0079] The transmission unit 10 b continues to output data until all ofthe signal levels of the second initialization pattern signal are outputto the transmission path 130 b (step S213).

[0080] When reception of the second initialization pattern signal andsetting of the evaluation levels (step S212) and transmission of thesecond initialization pattern signal (step S213) have been completed,the second data transmission apparatus 100 b is in the state where itcan perform transmission/reception of data (step S214).

[0081] The second initialization pattern signal transmitted from thesecond data transmission apparatus 100 b is received by the receptionunit 120 c of the third data transmission apparatus 100 c. When thesynchronization/initialization pattern detector 128 c detects thebeginning of the signal for recognizing the start of the secondinitialization pattern signal, the transmission data controller 129 coutputs a transmission data control signal instructing transmission ofthe second initialization pattern signal, to the selector 114 c of thetransmission unit 110 c (step S215)

[0082] When the reception unit 120 c receives the signal for recognizingthe start of the second initialization pattern signal and, further, thesecond initialization pattern signal, the evaluation level holding unit127 c sets the evaluation levels, and holds them (step S216).

[0083] When the transmission data control signal instructingtransmission of the second initialization pattern signal is input to theselector 114 c, the transmission unit 110 c transmits the secondinitialization pattern signal. That is, the selector 114 c selects thesecond initialization pattern signal generated by the secondinitialization pattern signal, and inputs this signal to the digitalfilter 115 c. Then, the transmission unit 110 c outputs the signal forrecognizing the start of the second initialization pattern signal, andthe second initialization pattern signal to the transmission path 130 cin like manner as for the first initialization pattern signal (stepS217).

[0084] When the reception unit 120 c receives all of the signal levelsof the second initialization pattern signal, and setting of theevaluation levels is completed, the transmission data controller 129 coutputs a transmission data control signal instructing transmission ofthe signal mapped in the data mapping unit 111 c, to the selector 114 cof the transmission unit 110 c (step S218).

[0085] Further, the transmission unit 110 c continues to output datauntil all of the signal levels of the second initialization patternsignal are output to the transmission path 130 c (step S219).

[0086] When reception of the second initialization pattern signal andsetting of the evaluation levels (step S218) and transmission of thesecond initialization pattern signal (step S219) have been completed,the third data transmission apparatus 100 c is in the state where it canperform transmission/reception of data (step S220).

[0087] The second initialization pattern signal transmitted from thethird data transmission apparatus 100 c is received by the receptionunit 120 a of the first data transmission apparatus 10 a (step S221).

[0088] When the reception unit 120 a receives the signal for recognizingthe start of the second initialization pattern signal and, further, thesecond initialization pattern signal, the evaluation level holding unit127 a sets the evaluation levels, and holds them (step S222).

[0089] When all of the signal levels of the second initializationpattern signal have been received, and setting of the evaluation levelshas been completed, the transmission data controller 129 a outputs atransmission data control signal instructing transmission of the signalthat is mapped in the data mapping unit 111 a to the selector 114 a ofthe transmission unit 110 a (step S223).

[0090] When transmission of the second initialization pattern signal(step S208) and reception of the second initialization pattern signaland setting of the evaluation levels (step S223) have been completed,the first data transmission apparatus 110 a is in the state where it canperform transmission/reception of data (step S224).

[0091] In this way, clock synchronization is established in all of thedata transmission apparatuses 100 a to 100 c connected in thering-shaped network, and the evaluation levels are set and stored.Thereafter, transmission data control signals instructing transmissionof the signals mapped in the data mapping units 111 a to 111 c are inputto the selectors 114 a to 114 c of the transmission units 111 a to 110c, whereby the selectors 114 a to 114 c select the signals from the datamapping units 111 a to 111 c as transmission signals. That is,transmission/reception of data is started, and the evaluation units 125a to 125 c evaluate the received data and decode the data symbols withreference to the evaluation levels stored in the evaluation levelholding units 127 a to 127 c.

[0092] As described above, the data transmission apparatus 100 accordingto the first embodiment is a data transmission apparatus connected in aring-shaped network, and the apparatus 100 is provided with the firstinitialization pattern output unit 112 for outputting the firstinitialization pattern signal to the next-stage data transmissionapparatus, the second initialization pattern generation unit 113 foroutputting the second initialization pattern signal to the next-stagedata transmission apparatus, and the synchronization establishment unit126 for receiving the first initialization pattern signal outputted fromthe previous-stage data transmission apparatus, and performing clockreproduction to establish synchronization. Since the data transmissionapparatus 100 starts transmission/reception of data aftersynchronization is established by the first initialization patternsignal and evaluation levels are set by the second initializationpattern signal, evaluation levels can be set after synchronization ofthe data transmission apparatus 100 is established. Further, sinceevaluation levels are set according to the voltage values of therespective signal levels included in the second initialization patternsignal, evaluation levels can be set in accordance with the transmissionpath, whereby accurate data reception can be carried out without beingaffected by the pattern of data symbols to be transmitted or the valuesof the received signal levels.

[0093] Furthermore, one of the data transmission apparatuses 100connected in the ring-shaped network is used as a master which outputsthe first initialization pattern signal at turn-on of power orimmediately after reset, and outputs the second initialization patternsignal by the second initialization pattern generator whensynchronization is established in all of the data transmissionapparatuses, while the other data transmission apparatuses 100 are usedas slaves which output the first initialization pattern signal from thefirst initialization pattern generator when synchronization isestablished, and output the second initialization pattern signal fromthe second initialization pattern generator on receipt of the beginningof the second initialization pattern signal, whereby the ring-shapednetwork can be initialized. Furthermore, since the slave can transmitthe second initialization pattern signal to the next-stage datatransmission apparatus upon receipt of the beginning of the secondinitialization pattern signal, setting of the evaluation levels andinitialization of the ring-shaped network can be carried out morespeedily.

[0094] Further, the first initialization pattern signal outputted fromthe first data transmission apparatus 100 a as a master is received bythe second data transmission apparatus 100 b as a slave to establishsynchronization. When synchronization is established, the second datatransmission apparatus 100 b outputs the first initialization patternsignal to the n-th data transmission apparatus 100 n in the next stage.When synchronization is established in all of the data transmissionapparatuses, the first data transmission apparatus 100 a outputs thesecond initialization pattern signal to the second data transmissionapparatus 100 b, and the second data transmission apparatus 100 breceives the second initialization pattern signal to set evaluationlevels, and outputs the second initialization pattern signal to the n-thdata transmission apparatus 100 n in the next stage. When setting ofevaluation levels is completed in all of the data transmissionapparatuses, transmission/reception of data is started. Therefore,synchronization in each data transmission apparatus can be established,and evaluation levels can be set. Further, since evaluation levels areset according to the voltage values of the respective signal levelsincluded in the second initialization pattern signal, evaluation levelscan be set in accordance with the transmission path, whereby accuratedata reception can be carried out without being affected by the patternof data symbols to be transmitted, and the values of the received signallevels.

[0095] Further, since the first initialization pattern signal is asignal in which a maximum amplitude level and a minimum amplitude levelappear alternately, clock synchronization can be established utilizingthe amplitude of the first initialization pattern signal received.

[0096] Furthermore, since the second initialization pattern signal is asignal in which all of the signal levels appear in an arrangement thatis predetermined by the transmission unit 110 and the reception unit120, all of the signal levels can be obtained without scrambling thesecond initialization pattern signal.

[0097] In the above description as shown in FIG. 3, 3-bit data aremapped to any of eight signal levels κ−7”, “−5”, “−3”, “−1”, “+1”, “+3”,“+5”, and “+7” according to their combinations by the data mapping unit111 of the data transmission apparatus 100. However, the presentinvention is not restricted to the above-described 8-value transmission,and arbitrary multi-valued transmission may be carried out.

[0098] Furthermore, differential mapping in which mapping of data to betransmitted is carried out according to the signal level that is mappedlast time, may be employed. In this case, evaluation of the signal levelis carried out on the basis of the difference between the signal levelthat is just received by the reception unit 120 and the signal levelthat is received last time, and the decoding is carried out. Also inthis case, the same effects as described above can be achieved byholding the evaluation levels based on the differences in the signallevels with the evaluation level holding unit.

APPLICABILITY IN INDUSTRY

[0099] The data transmission apparatus according to the presentinvention transmits an initialization pattern signal at turn-on of poweror immediately after reset, and performs establishment ofsynchronization and setting of evaluation levels on receipt of theinitialization pattern signal. Therefore, evaluation levels can be setin accordance with the transmission path, and establishment ofsynchronization and setting of evaluation levels can be carried out alsoin a ring-shaped network constituted by plural data transmissionapparatuses.

1. An initialization method to be used in a network in which pluralstages of data transmission apparatuses, each performing datatransmission while assigning one or more bits of data as one data symbolto a signal level, are connected in a ring shape, wherein one of thedata transmission apparatuses is a master data transmission apparatus,while the other data transmission apparatuses are slave datatransmission apparatuses; at turn-on of power or immediately afterreset, the master data transmission apparatus outputs a firstinitialization pattern signal to a slave data transmission apparatus inthe next stage; the next-stage slave data transmission apparatusestablishes clock synchronization on receipt of the first initializationpattern signal; when clock synchronization is established, thenext-stage slave data transmission apparatus outputs the firstinitialization pattern signal to a slave data transmission apparatus inthe next stage; when synchronization is established in all of the slavedata transmission apparatuses and the master data transmission apparatuswhich are connected in the network, the master data transmissionapparatus outputs a second initialization pattern signal to thenext-stage slave data transmission apparatus; the next-stage slave datatransmission apparatus receives the second initialization patternsignal, sets an evaluation level for each signal level, and outputs thesecond initialization pattern to a data transmission apparatus in thenext stage; and transmission/reception of data is started afterevaluation levels of data are set in all of the slave data transmissionapparatuses and the master data transmission apparatus which areconnected in the network.
 2. An initialization method as defined inclaim 1, wherein the first initialization pattern signal is a signal inwhich a maximum signal level and a minimum signal level appearalternately; and the second initialization pattern signal is a signal inwhich all signal levels appear in a predetermined arrangement.
 3. Aninitialization method as defined in claim 2, wherein the firstinitialization pattern signal is a signal in which a signal fordiscriminating between the first initialization pattern signal and thesecond initialization pattern signal appears at the end.
 4. Aninitialization method as defined in claim 2, wherein the secondinitialization pattern signal is a signal in which a signal fordiscriminating between the first initialization pattern signal and thesecond initialization pattern signal appears at the beginning.
 5. A datatransmission apparatus which is connected in a ring-shaped network, andperforms data transmission while assigning one or more bits of data asone data symbol to a signal level, said apparatus comprising: a firstinitialization pattern output unit for outputting a first initializationpattern signal for establishing clock synchronization to a datatransmission apparatus connected in the next stage; a secondinitialization pattern output unit for outputting a secondinitialization pattern signal for setting an evaluation level by whichthe signal level is subjected to threshold evaluation, to the datatransmission apparatus connected in the next stage; and asynchronization establishment unit for receiving the firstinitialization pattern signal transmitted from a data transmissionapparatus connected in the previous stage, and performing clockreproduction to establish synchronization; whereintransmission/reception of data is started after synchronization isestablished on receipt of the first initialization pattern signal, andevaluation levels of data are set on receipt of the secondinitialization pattern signal.
 6. A data transmission apparatus asdefined in claim 5 being a master data transmission apparatus in whichthe first initialization pattern output unit outputs the firstinitialization pattern signal at turn-on of power or immediately afterreset, and the second initialization pattern output unit outputs thesecond initialization pattern signal when synchronization is establishedin all of the data transmission apparatuses.
 7. A data transmissionapparatus as defined in claim 5 being a slave data transmissionapparatus in which the first initialization pattern output unit outputsthe first initialization pattern signal when synchronization isestablished, and the second initialization pattern output unit outputsthe second initialization pattern signal when the beginning of thesecond initialization pattern signal is received.